U.S. patent application Ser. Nos. '860 and '113, the disclosures of which are incorporated herein by reference, discloses and claims an improved wastewater treatment process referred to as I.D.E.A. "C.F.C.R." which is an acronym for "Intermittent Decant Extended Aeration Continuous Feed Cyclic Reactor" and incorporates CONTINUOUS FEED activated sludge technology with intermittent CYCLIC system operation requiring only a SINGLE BASIN. The system uses a single tank (reactor basin), preferably made of fiberglass in which the activated sludge is aerated over a number of pre-determined cycles. Solid/liquid separation occurs during the air-off cycle. Treated effluent is decanted or withdrawn from directly below the liquid surface. Influent inflow is continuously accommodated at all times. In this way the function of flow equalization, biological oxidation, nitrification, denitrification, secondary sedimentation and aerobic sludge digestion are all carried out in a single vessel. The duration of a cycle is specific to each design application and variable in the field as required.
The Continuous Feed Cyclic Reactor (C.F.C.R.) Process of the I.D.E.A. System combines SBR, ICEAS, and Continuous Flow Activated Sludge and Extended Aeration Principles. It is a fill and draw system which accommodates continuous feed (influent) to the tank (reactor basin). The heart of the process lies in the activated sludge blanket which reduces the BOD5 (biological oxygen demand) and TSS (total suspended solids) and removes nitrogen and phosphorous in the absence of polymers or filters. Food to microorganism ratios (F:M) may vary from 0.04 to 0.3 lb. of BOD5 /lb of MLSS/DAY and mixed liquor suspended solids (MLSS) design concentrations range from 1,000 to 15,000 mg/l. Actual practice has shown MLSS concentration in the 2,000 to 8,000 mg/l range to be most effective. With a hydraulic retention time (HRT) targeted for 18-36 hours and a sludge age (SRT) of at least 20 days. The Intermittent Decant Extended Aeration (I.D.E.A.) system is sized according to extended aeration standards. With such design parameters, typical excess solids (waste sludge) production ranges from 0.5 to 1.0 LB/LB of BOD5 removed. The sludge produced is quite stable with an O2 uptake rate of less than 10 mg/l O2/gm MLSS/hr.
One of the major process advantages of the Intermittent or Cycled Extended Aeration Process (EPA Design manual "0n Site Waste-Water Treatment and Disposal Systems", October 1980.) used in the I.D.E.A. System is that it provides nitrification/denitrification in addition to carbonaceous BOD5 reduction and solids removal without the addition of methanol as an organic carbon source. In addition, denitrification enhances alkalinity recovery. This prevents a PH drop which could contribute to filamentous growth and bulked sludge. Alkalinity recovery is particularly advantageous in regions of low natural alklinity.
It is this unique cyclic process which allows the I.D.E.A System to accomplish nitrification and denitrification. During aeration, biological oxidation and mixing occur. Blower sizing typically provides for 1.4 to 1.6 LBS. of O2/LB of BOD applied/day. For very low strength waste, 20 SCFM/1000 cubic feet reactor volume is provided for mixing. During aeration, excess oxygen is present, and Nitrosomonas sp. oxidize the Ammonia Nitrogen (N/NH3) to Nitrite Nitrogen (N/NO 2). Nitrobacter sp. further oxidize the Nitrite Nitrogen (N/NO2) to Nitrate Nitrogen (N/NO3). Both of these are naturally occurring bacteria as a result of this Cycled Extended Aeration "CFCR" Process.
Nitrate, Nitrite, Ammonia and Organic Nitrogen are all inter-related in wastewater. All of these forms of Nitrogen, as well as Nitrogen Gas are biochemically interconvertible. Ammonia is generally found in large quantities in fresh domestic wastewater, however Nitrate is found only in small amounts. But in the effluent of conventional Nitrifying biological treatment plants, Nitrate is found in concentrations of up to 50 mg/L Nitrate Nitrogen. Nitrite is an intermediate state of Nitrogen, both in the oxidation of Ammonia to Nitrate and in the reduction of Nitrate to Nitrogen Gas. Such oxidation occurs in the I.D.E.A. System.
During non-aerated periods (sedimentation and decantation), the Dissolved Oxygen (DO) level in the sludge blanket (MLSS) approaches zero. The lack of molecular oxygen (O2) encourages Pseudomonas sp. and other denitrifying bacteria to attack the oxygen bound up in the Nitrate (NO3) molecules. The bacteria then reduce the Nitrate (NO3) molecules to nitrogen (N2) and oxygen (O2). The molecular Nitrogen (N2), a gas, is released to the atmosphere, while the bacteria utilize the liberated Oxygen (O2). Thus, alternation of oxic and anoxic periods in the I.D.E.A. basin promotes Ammonia Nitrogen (N/NH3) removal from the waste stream of 95% or better.
Additional Nitrogen removal is accomplished through assimilation (absorption and incorporation) of Nitrogen into bacterial cell mass in satisfaction of metabolic needs. This Nitrogen is removed from the system when excess sludge is wasted from the I.D.E.A. basin. Actual operating data have shown the concentration of nitrogen in the sludge mass to be between 5% and 8% by weight of the dry solids. As can be seen, the nutrient removals and high degree of treatment characteristic of tertiary treatment systems can be had at the cost of an I.D.E.A. "CFCR" secondary treatment system.
While the '860 application teaches the above improved apparatus and method it teaches primarily a circular IVE collector and a circular partition to surround the IVE collector which substantially limits the ratio of the bottom open area around the skirt to the volume ratio inside. The primary advantage of the present improvement is to make the IVE collector and the partition which surrounds it in the form of a rectangular configuration in order to increase the skirt ratio to the inside volume ratio thus causing hydraulic flow equalization velocity flow reduction.
In the past, other attempts have been made which address the problem of hydraulic velocity such as U.S. Pat. No. 4,468,327 which provides an elongated tank having a length between 3.5 and 6 times the width thereof which requires decanting from the opposite end of the tank from it's inlet and also teaches a transverse baffle across the tank dividing the tank into a first portion adjacent the inlet and a second portion remote from the inlet. The volume ratio of said first portion to said second portion being between about 1;10 to about 1;3. The baffle wall is not adjustable but has an opening at or adjacent to the lower edge of the baffle wall to allow influent passing into the tank to pass through the openings and into the main body of the tank. In the event of a "storm flow" situation, which occurs often especially when using lift stations as a means of influent input, all of the influent must pass through these openings and has been the source of excessive hydraulic flow which disturbs the sludge blanket in the main tank. The '327 reference has no means to change the ratio of hydraulic flow as does the present improvement and invention. Also the method claims of the '327 reference requires at least one transverse baffle and decanting at a point remote from the inlet.
Also, the prior art such as is illustrated by the '327 reference in what is commonly called the "pre-react zone" allows the incoming influent to create downward velocities in the pre-react chamber which does not allow undisturbed settling of the sludge blanket in that chamber during the air off settle and decant phases of their cycle.
Also, a ratio of no less than 1-10 is required in the pre-react zone. With this capacity of 10% to 30% of the total volume this system encounters extremely high flow velocities during hydraulic equalization between the pre-react and the main react zones during the settle and decant phases.
During times that the system is receiving peak influent flows and decanting, these transfer velocities will be as much as 6 times greater than those of the present invention.
The prior art also has no means to variably control the hydraulic velocities at start up when the sludge blanket is relatively thin as compared to the sludge blanket when it reaches maturity.
Also, the prior art such as is illustrated by the '327 reference does not have a naturally bio-mass filtering action in the first chamber but is relying on the transfer underneath the sludge blanket in the second chamber, thus requiring decanting at as remote a distance as possible away from the output of the first chamber so as to allow upset sludge caused by hydraulic flows to again settle before reaching the decanter at the other end of the tank. This again causes hydraulic disturbance and excessive overflow velocities as all the effluent must travel the full distance of the second chamber to reach the decanter means. Unlike the present invention, the prior art such as is illustrated by the '327 reference, requires an elongated tank to get the decanting process as far away as possible from the incoming influent and states that they require a length of 3.5 to 6 times the width.